Information about the prevalence of disorders of the chemical senses has been limited. In the late 1970s, a consensus among experts convened by NIH was that more than 2 million adults in the U.S. had a disorder of smell or taste. A large, nonrandom survey conducted by the National Geographic Society in 1987 found that 1% of their 1.2 million respondents could not smell three or more of six odorants using a "scratch and sniff" test. Age was an important factor, with a decline beginning in the second decade of life. No comparable data has been available for taste, although it has been suggested that the sense of taste remains more robust with age. The Epidemiology Branch, NIDCD began collaborating with NCHS in 1993 to acquire information on the prevalence of smell and/or taste problems using the Disability Supplement to the National Health Interview Survey (NHIS). This survey was administered through personal interviews in over 45,000 randomly-selected households (more than 80,000 adults) in 1994. After adjusting for the complex survey design, we calculated an estimated national prevalence of 2.7 million (1.4%) adults with a chronic olfactory (sense of smell) problem. In this survey, "chronic" refers to a problem lasting at least three months during the past year. In addition, we calculated that 1.1 million (0.6%) adults in the U.S. had a chronic gustatory (taste) problem. When smell or taste problems were combined, 3.2 million (1.65%) adults in the U.S. were estimated to have a chronic chemosensory problem. The estimated prevalence rates increase markedly with age. Almost 40% of adults with a chemosensory problem (1.5 million) were greater than 65 years of age. In a multivariate analysis, we found overall health status, other sensory impairments, functional limitations (including difficulty standing or bending), depression, phobia, and several other health-related characteristics were associated with an increase in the rate of chemosensory disorders. Analyses were also performed on chronic problems with balance, as ascertained from responses to the household interview of the Disability Supplement to the NHIS. The Epidemiology Branch, NIDCD was also responsible for the formulation and inclusion of questions on dizziness, balance, and tinnitus (ringing in the ears) in the NHIS. Analyses have been conducted separately on reported chronic problems of dizziness versus balance. Although there is considerable overlap between the two conditions, chronic dizziness is relatively more common in younger adults, while chronic problems with balance is more frequently reported in older adults. The prevalence of chronic problems with balance increases steadily with age, from the youngest group (18-24 years old) to the oldest (75 years of age or older).